Throughout their history, attempts have been made to increase the efficiency of internal combustion engines. Although alternative and improved designs have been proposed, it is generally conceded that the spark ignition and diesel designs will still be the engines of choice for most ground and marine based systems.
Mass produced engines have relatively mediocre efficiency ratings--about 35-40%. The great bulk of these inefficiencies may be traced to wasted heat. Accordingly, some engine research has been directed toward harnessing heat otherwise lost to the block, coolant, radiator, exhaust system and ultimately to the environment.
One line of research has been the attempt to formalize low heat rejection engines (commonly but imprecisely called adiabatic engines). Although simple in theory--the "waste" heat is captured and converted to additional work--the practice has proven difficult. The major stumbling block has been the temperature limits of the engine component materials. Common materials such as cast iron, aluminum alloys, and many stainless steels cannot withstand the rigors of the higher engine temperatures contemplated with the newer designs. Ceramics and composites are brittle and are difficult to fashion into the appropriate shapes.
A novel compounded overcharged engine has been proposed in Canadian patent application filed on Sept. 12, 1989. A low heat rejection embodiment is discussed in this application.